1. Field of Invention
The invention relates to a control for a vehicle and, more particularly, to a deceleration control for the vehicle executed upon a coast downshifting operation, that is, downshifting operation of an automatic transmission performed in a coast state of the vehicle where the throttle valve is substantially fully closed.
2. Description of Related Art
There is known a vehicle that includes (a) an engine that generates power through combustion of fuel, and (b) an automatic transmission that transmits a reverse input from the driving wheel to the engine, and establishes a speed selected among a plurality of forward speeds each having a different speed ratio. A control apparatus disclosed in JP-A-11-278103, for example, executes a fuel cut control (F/C control) that interrupts supply of the fuel to the engine when a predetermined fuel cut (F/C) condition is satisfied, for example, when an engine speed becomes equal to or higher than a predetermined engine speed at release of the F/C control (hereinafter referred to as the F/C release engine speed). The aforementioned control apparatus increases the engine speed to expand a fuel cut range (vehicle speed range) by bringing a lock-up clutch of a torque converter into a slip engagement under the F/C control. When the lock-up clutch is engaged, the throttle valve is opened so as to prevent temporary increase in the engine braking force.
Even if the above-described control apparatus is employed in the vehicle, an inertia caused by the change in the engine speed may vary the engine braking force upon downshifting of the automatic transmission resulting from the decrease in the vehicle speed. This may cause a shock felt by the vehicle operator. In the case where the vehicle speed upon downshifting in the coast state (coast downshifting operation) is set to be a relatively higher value for continuing the F/C control, a range of the change in the engine speed resulting from the downshifting becomes wider, thus causing the vehicle operator to feel further shock.
In the case where the vehicle is running downhill, the engine braking force is increased to decelerate by performing the downshifting operation of the automatic transmission. This operation, however, may cause the engine braking force to temporarily become excessively large or fail to generate sufficient engine braking force, resulting in inappropriate deceleration control performance.